<glsl-doodle for="myDoodle" width="256" height="256"></glsl-doodle>
<script id="myDoodle" type="x-shader/x-fragment">
#ifdef GL_ES
precision mediump float;
#endif

uniform float dd_frameIndex;

void main() {
  gl_FragColor = (0.5 + 0.5 * sin(0.05 * dd_frameIndex)) * vec4(1, 0, 0, 1);
}
</script>